The invention pertains to methods and apparatus for tracking the gaze point of an eye.
Various systems have been developed for measuring head movement (xe2x80x9chead trackingxe2x80x9d) and the gaze of an eye (xe2x80x9cgaze point trackingxe2x80x9d) with respect to a video display terminal or other display device. In many such systems, a video signal corresponding to an image of a reference point is received as a video signal that is digitized and stored in a memory called a frame buffer. Because the video signal corresponding to a single image contains approximately 500 rows by 500 columns of individual pixel signals, a large memory is required for the frame buffer. The stored image is then processed to identify and locate objects within the image.
Image processing in this way has many drawbacks. First, an entire array of pixels for an image must be digitized and stored, requiring a large memory for the frame buffer. Processing the digitized image data is complex and it is difficult to identify images corresponding to the head or eye in the image. In addition, if image processing is to be fast enough to permit head or eye tracking, expensive signal processing systems are necessary. These problems are particularly severe in cost-sensitive applications. Accordingly, improved methods and apparatus are needed for simple, inexpensive image processing.
An apparatus for processing a video signal in a gaze point or head tracking system is provided. The apparatus comprises a comparator that receives a video signal at a first input and a reference signal from a reference source at a second input. The comparator produces a first output level at an output for portions of the video signal larger than the reference signal and a second output level for portions of the video signal less than the reference level, producing a processed video signal at the output.
A logical processor, such as a complex programmable logic device, receives the processed video signal and identifies xe2x80x9ceventsxe2x80x9d corresponding to transitions between the first and second output levels. Events are stored in a memory as event coordinates that locate the event in the image and a direction of transition (first to second or second to first output levels). If there is more than one video source or more than one reference signal, the events also contain a coordinate identifying the video source or reference level.
A video processor receives event coordinates and identifies objects as object coordinates. The objects are associated with features in, for example, an eye image or a beacon image. The object coordinates are processed to determine head location relative to a beacon or a direction of gaze of an eye. If the gaze point tracking apparatus is used in conjunction with a computer, object processing can be carried out by the computer. Alternatively, a separate processor can be provided.
A microcontroller is provided for adjusting the reference signal, or the reference signal can be adjusted manually.
In a gaze point tracking system used with a computer, video signals corresponding to both head and eye images are processed. A software component is provided that contains instructions for video processing and calibration. The calibration instructions permit the gaze point of a user""s eye to be associated with a position on display and a cursor to be displayed at the gaze point. After calibration, the gaze point is tracked as the eye and head move. Alternatively, only head movement or eye movement can be tracked.
The software component comprises a setup component that permits the user to associate various eye movements (including blinking) with instructions to the computer. In addition, the setup component permits the user to direct that the cursor be moved to coincide with the gaze point, or that the cursor be moved toward the gaze point. The setup component also permits the user to set a gaze point/cursor misalignment for which the cursor is not moved. This permits the cursor to remain fixed for small movements of the gaze point. In addition, the setup component can associate rapid or large movements of the gaze point with instructions to the computer. The software component can be provided on a computer readable medium, such as a CD-ROM.
Other features and advantages of the invention will be apparent from the following detailed description and accompanying drawings.